Pre-conditioned self-destructing substrate

ABSTRACT

A self-destructing device includes a frangible substrate having at least one pre-weakened area. A heater is thermally coupled to the frangible substrate proximate to or at the pre-weakened area. When activated, the heater generates heat sufficient to initiate self-destruction of the frangible substrate by fractures that propagate from the pre-weakened area and cause the frangible substrate to break into many pieces.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.15/299,385, filed Oct. 20, 2016, to which priority is claimed, and whichis incorporated herein by reference in its entirety.

RESEARCH AND DEVELOPMENT

This invention is based upon work supported by DARPA under Contract No.HR0011-14-C-0013 DARPA-MTO-VAPR-DUST. The Government has certain rightsto this invention.

TECHNICAL FIELD

This disclosure relates generally to devices comprising self-destructingsubstrates and to related methods and devices.

BACKGROUND

Electronic systems capable of physically self-destructing in acontrolled, triggerable manner are useful in a variety of applications,such as maintaining security and supply chain integrity.

BRIEF SUMMARY

A self-destructing device includes a frangible substrate having at leastone pre-weakened area. A heater is thermally coupled to the frangiblesubstrate proximate to or at the pre-weakened area. When activated, theheater generates heat sufficient to initiate self-destruction of thefrangible substrate by fractures that propagate from the pre-weakenedarea and cause the frangible substrate to break into many pieces.

Some embodiments are directed to self-destructing device comprising afrangible substrate having a pre-weakened area and a heater thermallycoupled to the frangible substrate proximate to or at the pre-weakenedarea. The device further includes a power source and trigger circuitry.The trigger circuitry includes a sensor and a switch. The sensorgenerates a trigger signal when exposed to a trigger stimulus. Theswitch couples the power source to the heater when actuated by thetrigger signal. When the heater is coupled to the power source, theheater generates heat sufficient to initiate self-destruction of thefrangible substrate by fractures propagating from the pre-weakened areaand causing the frangible substrate to break into many pieces.

Some embodiments are directed to a method involving a frangiblesubstrate. The method includes disposing a heater on a frangiblesubstrate such that the heater is thermally coupled to the frangiblesubstrate. The frangible substrate is pre-conditioned at or proximate toa location of the heater to form a pre-weakened area. Thepre-conditioning weakens the substrate at the pre-weakened area withoutcausing self-destruction of the frangible substrate such that subsequentapplication of a predetermined level of energy to the heater causes theself-destruction of the frangible substrate due to fractures topropagating from the pre-weakened area.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows self-destructing device configured to self-destruct inresponse to a exposure to energy in accordance with some embodiments;

FIG. 2 shows a self-destructing device that also includes an energysource for activating the heater in accordance with some embodiments;

FIGS. 3A through 3C are cross sectional diagrams of frangible substratesin accordance with some embodiments;

FIG. 4 is a diagram illustrating a self-destructing device that includesan energy source and trigger circuitry in accordance with someembodiments;

FIG. 5 is a flow diagram illustrating a method of using theself-destructing device of FIG. 4

FIG. 6 is a diagram of a self-destructing device comprising aself-limiting resistive heater disposed on a frangible substrate inaccordance with some embodiments;

FIG. 7 is a flow diagram showing a generalized method for triggeringself-destruction of the self-destructing device illustrated in FIG. 6 ;

FIG. 8 is a perspective view showing a portion of a self-destructingdevice having a self-limiting resistive element comprising a fuse-typecurrent-limiting portion connected in series between two resistiveportions in accordance with some embodiments;

FIGS. 9 and 10 are top plan views showing self-limiting resistiveelements that comprise patterned metal layer structures disposeddirectly on upper surfaces of frangible substrates in accordance withsome embodiments;

FIG. 11 is a circuit diagram showing a self-destructing device includinga remotely (wirelessly) controllable trigger mechanism including asensor configured to sense the presence and/or amount of a triggerstimulus in accordance with some embodiments;

FIGS. 12A and 12B show simplified transient electronic devices in whichsensor and/or switch elements are either fabricated or mounted directlyon the frangible substrate or are fabricated concurrently with theelectronic elements on a semiconductor layer according to someembodiments.

FIG. 13A is a cross sectional view of a p-i-n photodiode that may beused as the sensor of a self-destructing device in accordance with someembodiments.

FIG. 13B is a top view of the p-i-n photodiode of FIG. 13A;

FIG. 14 shows the photocurrent response when the 3 mm×3 mm photodetectoris in the dark, exposed to ambient light in a bright fluorescent-litroom, illuminated with a bright cell phone LED flashlight at closeproximity, and when illuminated with a typical 5 mW green laser pointerin accordance with some embodiments;

FIG. 15 is a flow diagram that illustrates a process of making thephotodetector in accordance with some embodiments;

FIGS. 16A and 16B diagrammatically depict top views that illustrate theprocess of making the photodetector in accordance with some embodiments;

FIG. 17 shows the example device comprising a frangible substrate andtwo integrated heaters disposed at opposite ends of the substrate inaccordance with some embodiments;

FIG. 18 shows the electrical trace signals of a pulse used to conditiona heater shown in FIG. 17 and the voltage across the heater;

FIG. 19 shows the electrical characteristics of the heater of FIGS. 17and 18 after the substrate has been pre-weakened when the heater isoperated so the applied stimulus causes the heater to fuse and thesubstrate to fracture.

The figures are not necessarily to scale. Like numbers used in thefigures refer to like components. However, it will be understood thatthe use of a number to refer to a component in a given figure is notintended to limit the component in another figure labeled with the samenumber.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments disclosed herein relate to devices capable ofself-destructing by fracturing into small pieces in a controlled,triggerable manner. Devices and methods disclosed herein are useful in avariety of applications such as government security and supply chainintegrity. Devices discussed herein are capable of self-destructing intosmall pieces when a heater is activated by an energy source, e.g., asource supplying optical, electrical, microwave energy. Activation ofthe heater can consume a substantial amount of energy when causing thesubstrate to self-destruct. Embodiments described herein involve adevice that includes a frangible substrate having a pre-weakened areathat reduces the energy required to cause the substrate toself-destruct.

FIG. 1 shows self-destructing device 100 configured to self-destruct inresponse to exposure to an energy source. Self-destructing device 100includes a frangible substrate 110 having at least one previouslydamaged area 111. A heater 120 is thermally coupled to the frangiblesubstrate 110 at a location 112 at or proximate to the damaged area 111.One or more components 150, e.g., electronic circuits, may also bedisposed on the substrate 110. In some embodiments, the heater is aresistive conductive film that is energized by flowing electricalcurrent. In some embodiments, the heater 120 may a radio-frequencyabsorber energized by radio-frequency source. In yet other embodiments,the heater 120 may an optical absorber energized by a laser beam. Insome embodiments, the heater 120 can be a resistive conductive filmcomprising a thin film fuse that breaks when the temperature of the thinfilm fuse reaches a sufficiently high value.

FIG. 2 shows a self-destructing device 200 that also includes an energysource 140. The energy source 140 may supply optical, microwave, and/orelectrical energy to activate the heater. When activated by the energysource 140, the heater 120 absorbs or generates heat and transfers theheat to the frangible substrate 110. The heat from the heater 120 issufficient to cause the frangible substrate 110 with the pre-weakenedarea 111 to self-destruct by fracturing into many small pieces, e.g.,using a mechanism similar to that captured in a Prince Rupert's Drop. Insome embodiments, the fracture dynamics are designed so that thefrangible substrate 110 self-destructs by fracturing into smallparticles such that most of the particles have length, width, and heightdimensions of less than about 900 μm, less than about 500 μm, or evenless than about 100 μm. In addition, the released potential energyduring self-destruction of the substrate 110 can be sufficient to alsocause the heater 120, components 150 and any other structures disposedon substrate 110 to fracture into small pieces.

The pre-weakened area 111 is configured such that the threshold energyimparted to the heater 120 that initiates self-destruction of thefrangible substrate 110 having the pre-weakened area 111 may be lessthan about 60%, or less than about 40% but greater than 5% of athreshold energy that initiates self-destruction of a similar frangiblesubstrate without the pre-weakened area.

In some embodiments, as shown in the cross sectional diagram of FIG. 3A,frangible substrate 310 a includes at least one glass structureincluding a first glass material having a first coefficient of thermalexpansion (CIE) value, and multiple second glass structures 312 a, 313 arespectively including one or more different (second) glass materialsrespectively having a second CTE value, where the second CTE value isdifferent from the first CTE value. For example thermally tempered glasssubstrate 310 a includes a glass structure 311 a disposed between twoglass structures 312 a and 313 a, where glass structure 311 a comprisesa different glass material having a different CTE value than the glassmaterial from which glass structures 312 a and 313 a are formed.

In some embodiments, as shown in the cross sectional diagram of FIG. 3B,a frangible substrate 310 b comprises thermally tempered glass. Thethermally tempered glass substrate 310 b includes second glassstructures 312 b disposed in a first glass structure 311 b, where glassstructure 311 b comprises a different glass material than that of glassstructures 312 b. The fabrication of such thermally tempered glasssubstrates is described in U.S. Pub. App. No. 2015/0358021, which isincorporated herein by reference in its entirety.

In some embodiments, a frangible substrate 310 c comprisesstress-engineered tensile 311 c and compressive 312 c layers that areoperably attached together as illustrated in the cross sectional diagramof FIG. 3C. The at least one tensile stress layer 311 c has a residualtensile stress and the at least one compressive stress layer 312 c has aresidual compressive stress. Tensile stress layer 311 c and compressivestress layer 312 c (collectively referred to herein as“stress-engineered layers”) can be operably integrally connectedtogether such that residual tensile and compressive stresses areself-equilibrating and produce a stress gradient. The stress-engineeredlayers 311 c, 312 c may be fabricated either by post-treating asubstrate material using strategies similar to glass tempering (e.g., byway of heat or chemical treatment), or by depositing the substratelayers using, for example chemical, vapor deposition techniques in whichthe deposition parameters (i.e., temperature, pressure, chemistry) arevaried such that the layers collectively contain a significant inbuiltstress gradient. Fabrication of stress-engineered layers is described inin the manner described in U.S. Pat. No. 9,154,138 which is incorporatedherein by reference in its entirety. Note that the arrangement ofstress-engineered layers 311 c, 312 c indicated in FIG. 3C is notintended to be limiting in that one or more stressed and/ornon-frangible substrate layers may be disposed on and/or between the twostress-engineered layers 311 c, 312 c.

In yet another embodiment, a substrate may comprise an ion-exchangetreated glass substrate or interposer fabricated in the manner describedin U.S. patent application Ser. No. 14/694,132 filed Apr. 23, 2015 andentitled “Transient Electronic Device With Ion-Exchanged Glass TreatedInterposer” which is also incorporated herein by reference in itsentirety.

Returning now to FIG. 1 , in some embodiments, at least one of the oneor more components 150 may comprise electronic elements 152 fabricatedon a semiconductor base layer 151 such as a silicon on insulator (SOI)layer or an integrated circuit (IC) die/chip that is attached to asurface 113 of the frangible substrate 110. In some embodiments,components 150 may comprise electronic circuits 152 fabricated on asuitable semiconductor (base) layer 151 using existing IC fabricationtechniques, e.g., CMOS.

A device comprising a self-destructing substrate as discussed herein maybe employed to also destroy an IC or other component for purposes ofprotecting the environment or maintaining confidentiality, e.g.,preventing tampering and/or unauthorized reverse engineering of the ICor component. Fabricating an electronic component 150 on a frangiblesubstrate 110 facilitates forming the components 150 using low costmanufacturing techniques, and facilitates reliable elimination of thecomponents 150 by way of causing self-destruction of the frangiblesubstrate 110. The components 150 may be configured to perform aprescribed useful function (e.g., sensor operations) up until thedestruction of the frangible substrate 110 and components 150.

In some embodiments, the semiconductor layer 151 is a silicon “chip”(die) upon which electronic elements 152 are fabricated, and then thesemiconductor layer 151 is fixedly attached to the frangible substrate110 using a die bonding technique, such as anodic bonding, or by way ofsealing glass, that assures coincident destruction of electronicelements 152 with frangible substrate 110. In some embodiments, at leastone component 150 includes electronic elements 152 configured to form anIC device using standard silicon-on-insulator (SOI) fabricationtechniques, e.g., such that the at least one component 150 isimplemented as an SOI integrated circuit structure. In anotherembodiment, electronic elements 152 may be fabricated on an IC die thatis “thinned” (e.g., subjected to chemical mechanical polishing) beforethe IC die is bonded to the surface 113.

As shown in FIG. 4 , in some embodiments, a self-destructing device 400includes an energy source 140 and trigger circuitry 130 comprising asensor 131 and a switch 132. When the sensor 131 senses the triggerstimuli, the sensor 131 generates a trigger signal that actuates theswitch 132 to turn on an energy source 140 that activates the heater120. As shown in FIG. 4 , in response to sensing trigger stimulus, thesensor 131 actuates the switch 132. Actuation of the switch 132 connectsthe energy source 140 to a power circuit between +V, −V. The energysource is turned on and imparts energy to the heater. As previouslydiscussed, the energy source 140 may be an optical source, RF source, anelectrical current source, or other type of energy source.

The sensor 131 may be configured to sense to a variety of triggerstimuli, such as electromagnetic radiation (e.g., radio frequency (RF)radiation, infrared (IR radiation), visible light, ultraviolet (UV)radiation, x-ray radiation, etc.), vibration, a chemical, vapor, gas,sound, temperature, time, moisture, an environmental condition, etc. Forembodiments in which the trigger stimulus is visible light, the sensormay be configured to generate the trigger signal in response to exposureto broadband light, such as sunlight or room light, or narrow bandlight, such as green, red, or blue visible light. For example, thegreen, red or blue light may be produced by a laser.

In some embodiments, the sensor 131 is configured to detect a tamperingevent. For example, the tampering event can be detected when the deviceis exposed to a chemical used for removal of a package cover, the deviceis vibrated above a threshold vibration, and/or snooping with x-raysthat occurs.

In some embodiments, the sensor 131 senses time from a clock. When atimer goes off, an electrical trigger signal is generated to trigger theswitch 132.

FIG. 5 is a flow diagram illustrating a method of using theself-destructing device 400 shown in FIG. 4 . A pre-weakened frangiblesubstrate is provided 510, the pre-weakened frangible substrate havingone or more pre-weakened areas at or near a location of a heaterdisposed on the frangible substrate. The frangible substrate is damagedat the pre-weakened areas, but is still intact. A trigger signal isgenerated 520 in response to a trigger stimulus. The trigger signalturns on 530 the energy source that activates 540 the heater. The heaterheats 550 at least a portion of the pre-weakened area of the frangiblesubstrate. The heating of the frangible substrate produces a rapidrelease of stored mechanical energy via substrate fracture causing thefrangible substrate to self-destruct 560 by fracturing into many smallpieces, Self-destruction of the frangible substrate may also cause theheater and/or other components disposed on the frangible substrate toself-destruct by fracturing into many small pieces. In some embodiments,a subsequent cooling after the heating stage initiates the propagatingfractures in the frangible substrate that causes the frangible substrateto self-destruct.

Referring again to FIG. 4 , in some embodiments, the pre-conditioning ofthe frangible substrate 110 may be accomplished by a first type ofenergy and the self-destruction of the substrate 110 is caused by asecond type of energy. In various embodiments, the damaged area 111 ofthe frangible substrate 110 may be chemically, optically, mechanically,and/or thermally pre-weakened prior to placement of the heater 120 onthe frangible substrate 110. For example, the frangible substrate 110may be optically pre-weakened in the pre-weakened area by one or more oflaser ablation and laser drilling, wherein the surface 113 of thefrangible substrate 110 is exposed to an intense laser beam or to acontrolled laser pulse. The frangible substrate 110 may be mechanicallypre-weakened in the pre-weakened area 111 by one or more of controlledmechanical contact, e.g., an impact or physical removal of material fromthe frangible substrate 110, by scoring, machining, and/or abrasion ofthe surface 113 of the frangible substrate 110. The frangible substrate110 may be chemically pre-weakened in the pre-weakened area 111 bycontrolled exposure of the frangible substrate 110 to one or morechemicals, e.g., liquids, gasses, and/or plasma, that etch and/or pitthe frangible substrate 110. The frangible substrate 110 may bepre-weakened in the pre-weakened area 111 by controlled exposure to ofthe frangible substrate 110 to an electron beam, an electrical currentand/or an electrical voltage. The frangible substrate 110 may bethermally damaged at the pre-weakened area 111 by controlled exposure ofthe frangible substrate 110 to heat prior to and/or after placement ofthe heater 120 on the frangible substrate 110. The frangible substratemay be pre-conditioned by forming pits, holes, and/or patterns on thesubstrate by one or more of chemical etching, plasma etching, ionmilling, physical machining, and laser ablating the frangible substrate.

After placement of the heater 120, an energy source, e.g., an optical,electrical, radio frequency and/or microwave energy source, is triggeredthat activates the heater 120, causing the heater to heats at least aportion of the pre-weakened area 111. Heating of the pre-weakened arealeads to the self-destruction of the frangible substrate 110 asdiscussed herein. The heater 120 heats at least a portion of thepre-weakened area 111 to a threshold level sufficient to cause thesubstrate to self-destruct. For example, the heating to the thresholdlevel may involve heating the pre-weakened frangible substrate 110 to apredetermined temperature for a predetermined period of time. Heatingthe frangible substrate 110 to the threshold level produces propagatingfractures in the frangible substrate 110 that causes the—frangiblesubstrate to self-destruct by breaking apart into many pieces. Ifadditional components, e.g., electronic components 150, are present onthe frangible substrate, the additional components are destroyed byfracturing into many pieces along with the substrate.

In some embodiments, the frangible substrate 110 may pre-weakened usingthe same type of energy that causes self-destruction of the frangiblesubstrate 110. For example, after a resistive heater 120 is disposed onthe frangible substrate 110, one or more controlled current pulses fromthe a current source 140 activates the heater causing heater 120 to heatthe substrate 110. The heat caused by the controlled current pulses issufficient to cause damage to the substrate 110 at or near the locationof the heater 120 but is insufficient to cause the substrate 110 toself-destruct. The frangible substrate 110 may be pre-weakened byactivating the heater 120 at an energy lower than the threshold energyneeded to cause self-destruction of a similar frangible substrate thatdoes not include a damaged area.

After the pre-conditioning step, the resistive heater 120 is againactivated by the current source and the heater heats at least a portionof the pre-weakened area, the heat producing propagating fractures inthe frangible substrate 100 that cause the—frangible substrate 110 toself-destruct by breaking apart into many pieces. If additionalcomponents, e.g., electronic components 150, are present on thefrangible substrate 110, the additional components 150 may also bedestroyed by fracturing into many pieces along with the frangiblesubstrate 110.

In embodiments wherein the heater 120 is a resistive heater, thepre-weakened area 111 may be formed by activating the resistive heater120 by one or more damaging current pulses, each of the damaging currentpulses having a predetermined amplitude and a predetermined duration.The amplitude and/or duration of each damaging current pulse may be thesame, or the amplitude and/or duration of one or more of the damagingcurrent pulses may be different from the amplitude and/or duration ofone or more other damaging current pulses. In some implementations, thethermal energy generated by the damaging current pulses to damage thefrangible substrate 110 in the pre-weakened area 111 may be more thanabout 40% or more than about 60% but less than about 90% of thethreshold energy generated by current pulses that cause a similarfrangible substrate without a pre-weakened area to self-destruct. Insome implementations, the amplitude and/or time duration of the damagingcurrent pulses may be the same as the amplitude and/or duration ofsubsequent current pulses that cause the frangible substrate 110 havingthe damaged area 111 to self-destruct. The number of damaging currentpulses used to damage the pre-weakened area 111 may be more than about40% or more than about 60% but less than about 90% of the number ofcurrent pulses cause that cause a similar frangible substrate without apre-weakened area to self-destruct.

The self-destructing device 600 shown in the block diagram of FIG. 6comprises a self-limiting resistive heater 620 disposed on a frangiblesubstrate 110 and a trigger mechanism 630 comprising a sensor 631 and aswitch element 632. As depicted in FIG. 6 , the heater 620 is disposedon a frangible substrate 110 having a pre-weakened area 111 at orproximate to the resistive heater 620. The heater 620 is electricallyconnected between a first terminal (+) of a power supply 660 and a firstterminal 632-1 of the switch element 632. The second terminal 632-2 ofthe switch element 632 is electrically connected to the second terminal(−) of the power supply 660. A control terminal 632-3 of the switchelement 632 is operably disposed to receive an electronic trigger signalTS, which may be generated by an sensor 631 or other control circuitry(not shown). The switch element 632 is actuated (switched from anopen/non-conducting state to a closed/conducting state) by assertingtrigger signal at the control terminal 632-3 of the switch element 632.Actuation of the switch element 632 initiates a current I_(T) that flowsfrom the power supply 660 through self-limiting resistive element 620.In one embodiment, self-limiting resistive element 620 includes aresistive portion 662 and a current-limiting portion 665 that areconnected in series between the positive and negative terminals of thepower supply 660. One or both of the resistive portion 662 and acurrent-limiting portion 665 operably thermally coupled to frangibleglass substrate 110 such that self-limiting resistive element 620generates heat at a rate that rapidly increases a temperature of alocalized region 611 of the substrate 110 wherein the localized region611 includes at least a portion of the pre-weakened area 111. Thecurrent limiting portion 665 of the resistive heater 620 is furtherconfigured to independently control (e.g., without requiring anexternally-generated control signal) the flow of trigger current I_(T)by way of terminating the flow of trigger current I_(T) after localizedregion 611 receives a sufficiently large amount of the heat generated byself-limiting resistive element 620. In some embodiments, thecurrent-limiting portion 665 of the heater 620 is implemented by a fuseelement configured to fail (melt and break) after conducting apredetermined amount of trigger current I_(T) (e.g., after apredetermined amount of heat is generated by self-limiting resistiveelement 620). In some embodiments, current-limiting portion 665 may beimplemented by other elements/circuits configured to implement thedescribed independent control over trigger current I_(T), such as athermistor-based circuit configured to terminate the trigger currentflow upon detecting a predetermined temperature level, or a timer-basedcircuit configured to terminate the trigger current flow a preset timeafter actuation of switch element 632.

FIG. 7 is a flow diagram showing a generalized method for triggeringself-destruction of a self-destructing device 600 as shown in FIG. 6 inaccordance with some embodiments. Initially, the device 600 operatesnormally such that the components 150 disposed on the frangiblesubstrate 110 perform as intended. During normal operation, the switchelement 632 is in the open, non-conducting state and no current passesfrom the power supply 660 through self-limiting resistive element 620,and thus no heat is generated by resistive portion 662. Initially, thelocalized temperature in region 611 is about the same as the temperatureof regions of the frangible substrate 110 adjacent to region 611.

Self-destruction of the frangible substrate is initiated at a time, forexample, when a trigger stimulus is detected by a sensor e.g., inresponse to a wirelessly transmitted light or RF signal), orunauthorized tampering is detected. In response to the trigger stimulus,the trigger signal (TS) is asserted and applied to the control terminal632-3 of switch element 632, whereby the switch element 632 is actuated710 to initiate the flow of trigger current I_(T) through resistiveportion 662 and current control portion 665 to ground, whereby resistiveportion 662 begins to generate heat that is transmitted through uppersurface 111 of frangible substrate 110 into localized region 611 thatincludes at least a portion of the damaged area 111. The heat causes thelocalized temperature in the region 611 and pre-weakened area 111 toincrease above the initial temperature.

Subsequently, the continued flow of trigger current I_(T) causesresistive portion 662 to generate heat a rate that rapidly increases 720the localized temperature in at least a portion of the damaged area 111toward a predetermined target temperature T₁. According to someembodiments, this rapid temperature increase occurs at a rate thatcauses the temperature in the pre-weakened area 111 to increase at arate faster than the temperature in regions surrounding the localizedregion. The heat generated by the self-limiting resistive element 620enters the pre-weakened area 111 at a faster rate than dissipating heatleaves damaged area 111 into surrounding regions, thereby causing thetemperature of the pre-weakened area 111 to rapidly increase from theinitial temperature toward the higher target (first) temperature levelT₁ while surrounding regions remain at a substantially lowertemperature.

After the current flows I_(T) for a period of time, current limitingportion 665 actuates 730 to terminate the generation of heat by way offusing (breaking), creating an open circuit condition that terminatesthe flow of current through resistive portion 662. According to anotheraspect of the invention, self-limiting resistive element 620 isconfigured such that the termination of generated heat causes a rapiddecrease of temperature in the pre-weakened area 111 toward a lower(second) temperature T₂ by way of heat dissipating out of damaged areainto cooler regions surrounding the region 611. The thermal pulsegenerated 740 by the rapid temperature increase and rapid temperaturedecrease described above produces a stress profile in the pre-weakenedarea 111 of frangible substrate 110 that is sufficient to causepropagation of one or more fractures in the damaged area 111.Subsequently, propagating fractures radiate 750 from the pre-weakenedarea throughout frangible substrate 110, heater 620, and/or components150, thereby causing the self-destruction of the device 600.

A threshold level of thermal energy provided by the thermal pulsegenerates propagating fractures in the device 600 whereas energiesprovided that are below the threshold level do not generate propagatingfractures. The threshold energy of the thermal pulse that generates thepropagating fractures that cause the self-destruction of device 600having the pre-weakened area 111 is less than the threshold energy ofthe thermal pulse that generates propagating fractures that causeself-destruction of a similar device that does not have a pre-weakenedarea. For example, the amplitude, time duration, and/or product of theamplitude and time duration of a thermal pulse that creates propagatingfractures that cause device 600 to self-destruct may be more than about10% and less than about 60% or less than about 40% of the amplitude,time duration, and/or product of the amplitude and time duration of athermal pulse that generates fractures in a similar device that does notinclude a damaged area.

FIG. 8 is a perspective view showing a portion of a self-destructingdevice 800 having a self-limiting resistive element 820 comprising afuse-type current-limiting portion 825 connected in series between two(first and second) resistor structures (resistive portions) 822-1 and822-2, which are respectively connected to opposing (first and second)terminals 821-1, 821-2 and disposed over pre-weakened area 111. Whenoperably connected together, terminal 821-1 is coupled to a firstterminal of a power source (not shown) and terminal 821-2 is coupled byway of a switch element (not shown) to a second terminal of the powersource. In some embodiments, resistor structures 822-1, 822-2 andfuse-type current-limiting portion 825 are produced by depositing asingle (common) resistive material (e.g., one or more of magnesium,copper, tungsten, aluminum, molybdenum and chrome) directly onto uppersurface 113 of frangible substrate 110. The resistive material issufficiently conductive and adheres to upper surface 113 of frangiblesubstrate 110 well enough that heat generated by resistive portions822-1, 822-2 and current-limiting portion 825 is transferred efficientlyinto pre-weakened area 111 during the rapid heating process of a thermalpulse. The resistive material is printed, etched or otherwise patternedsuch that resistor structures 822-1, 822-2 respectively compriserelatively large structures and fuse-type current-limiting portion 825comprises a relatively narrow thin structure configured to function as afuse element. When a sufficiently large current passes between terminals821-1, 821-2, resistor structures 822-1, 822-2 and current-limitingportion 825 undergo resistive heating, but its relatively narrowcross-section causes current-limiting portion 825 to produce a highertemperature, which is sufficient to cause melting and breakage whensubjected to a suitable trigger current. Implementing current-limitingportion 845 using a fuse-type current-limiting portion (fuse element)provides a low-cost, simple and highly reliable structure forindependently controlling the amount of heat generated by self-limitingresistive element 820 during the rapid heating process of a thermalpulse, and reliably produces an open circuit condition (i.e., by way ofmelting/breaking) that terminates flow of trigger current throughresistor structures 822-1 and 822-2 at the start of the rapid coolingportion of the thermal pulse.

FIGS. 9 and 10 are top plan views showing self-limiting resistiveelements 920 and 1020, each resistive element 920, 1020 comprises apatterned metal layer structure disposed directly on upper surfaces 913,1013 of frangible substrates 910, 1010. Pre-weakened areas 911, 1011 ofthe frangible substrates 910, 1010 are disposed proximate to theself-limiting resistive elements 920, 1020. Each resistive element 920,1020 includes a fuse element 925, 1025 connected between taperedsections 923-1, 923-2, 1023-1, 1023-2 of two resistor structures 922-1,922-2, 1022-1, 1022-2. For example, self-limiting resistive element 920includes a first resistor structure 922-1 including a tapered section923-1, a second resistor structure 922-2 including a tapered section923-2, and a fuse element 925 connected between the tapered ends oftapered sections 923-1, 923-2. Similarly, self-limiting resistiveelement 1020 includes a first resistor structure 1022-1 including atapered section 1023-1, a second resistor structure 1022-2 including atapered section 1023-2, and a fuse element 1025 connected betweentapered ends of the tapered sections 1023-1, 1023-2. In each case, fuseelements 925 and 1025 comprise narrow neck structures having widths W1that are configured to melt and break when subjected to a triggercurrent. In some embodiments, width W1 is greater than a thicknessfrangible substrate 110 (e.g., thickness T shown in FIG. 8 ). Forexample, in a some embodiments using a 0.25 mm thick frangiblesubstrate, fuse elements 925 and 1025 have widths W1 of at least 0.3 mm.In contrast, the resistor structures of both self-limiting resistiveelements (e.g., resistor structure 922-1) can have almost any width(size) W2, although larger resistors require more power and energy fromthe power source.

As depicted by the embodiments shown in FIGS. 9 and 10 , different fuseconfigurations may be utilized to generate desired thermal pulsecharacteristics. Specifically, self-limiting resistive elements 920 and1020 differ in that fuse element 925 comprises a straight rectangularstructure extending between tapered ends of the tapered sections 923-1,923-2, and fuse element 1025 comprises an S-shaped structure extendingbetween tapered ends of tapered sections 1023-1, 1023-2. These differentfuse arrangements provide different thermal characteristics, by allowingcontrol over the applied energy and power by tuning the resistance ofthe resistive elements 920, 1020 as well as tuning the area over whichthe heat is applied which can impact the time to fragment. Additionalinformation related to self-limiting electrical triggering forinitiating fracture of a frangible substrate is discussed in U.S. patentapplication Ser. No. 15/220,164 filed on Jul. 26, 2016 which isincorporated herein by reference.

FIG. 11 is a circuit diagram showing a self-destructing device 1100including a remotely (wirelessly) controllable trigger mechanism 1130including a sensor 1131 configured to sense the presence and/or amountof a trigger stimulus 1199 (e.g., presence of light, radio frequency(RF) signal, vibration, acoustic signal, chemical, etc.), and configuredto then generate the electronic trigger signal TS used to actuate theswitch element 1132. The self-destructing device 1100 includes aresistive heater 1120 thermally coupled to a frangible substrate havinga pre-weakened area (not shown). In some embodiments, the resistiveheater 1120 comprises a self-limiting resistive element comprising afuse element 1125 connected between a first resistor structure 1122-1and a second resistor structure 1122-2 as previously discussed inconnection with FIGS. 9 and 10 .

In an exemplary embodiment, switch element 1132 is implemented using asilicon controlled rectifier, the trigger stimulus is the presence oflight, and sensor 1131 is s a photodiode (or other light-sensitivedevice) operably coupled to switch element 1132. Current throughphotodiode 1131 actuates switch element 1132 by way of utilizing thecurrent to cause the silicon controlled rectifier to latch. Latching thesilicon controlled rectifier in turn couples the power supply 1140,e.g., a battery, across resistive heater 1120, ultimately causingself-destruction (fragmentation) of the frangible substrate and anyincluded electronics in the manner described above. While remoteactuation of the transient electronic device is achieved by the presenceof light in this example, other types of trigger stimuli, e.g., thepresence of electromagnetic radiation, vibration, sound, chemicals,temperature, etc. may be utilized by replacing photodiode with asuitable sensor for sensing the trigger stimuli. Similarly, whilelatching is achieved using silicon controlled rectifier in theembodiment illustrated by FIG. 11 , other switch elements may also beutilized, such as a latch circuit comprising a single MOSFET transistoror a MOSFET-based multiple-element circuit.

FIGS. 12A and 12B show simplified transient electronic devices 1200 aand 1200 b according to some embodiments in which sensor and/or switchelements are either fabricated or mounted directly on the frangiblesubstrate, or fabricated concurrently with the electronic elements on asemiconductor layer. For example, FIG. 12A shows a device 1200 a inwhich a sensor 1231 a (e.g., a photodiode) and a switch element 1232 a(e.g., a silicon controlled rectifier) are implemented by suitablematerials printed or patterned directly onto surface 1213 a of frangiblesubstrate 1210 a. Alternatively, as shown in FIG. 12B device 1200 bincludes a sensor 1231 b and a switch element 1232 b fabricated usingCMOS fabrication techniques on a semiconductor structure 1214 b (e.g.,IC chip or SOI layer) on which the electronic elements 1250 b areformed. In both embodiments, heater elements 1220 a, 1220 b are formeddirectly on frangible substrates 1210 a, 1210 b, respectively. Thefrangible substrates 1210 a, 1212 b include pre-weakened areas 1211 a,1211 b at or near the locations of the heater elements 1220 a, 1220 b.In some embodiments (not shown), one or both of the sensor and switchelement may be disposed on a host PC board and connected by way ofsuitable conductive connection to the heater element 1220 a, 1220 b.

As discussed above, in many embodiments, the sensor that senses thetrigger stimuli is a photodiode, e.g., a pn junction diode or p-i-ndiode, and the trigger signal is a photocurrent generated by thephotodiode in response to visible light or other electromagneticradiation. FIG. 13A is a cross sectional view and FIG. 13B is a top viewof a p-i-n photodiode sensor 1300 that may be used as the sensor of aself-destructing device in accordance with some embodiments.

The photodiode 1300 comprises a first electrode layer 1320 disposed overthe frangible substrate 1310. The first electrode layer 1320 extendsover the substrate 1310 to form a first lead 1333 of the photodiode1300. A first doped layer 1330, e.g., an n-doped amorphous siliconlayer, is disposed over the first electrode layer 1320. An intrinsiclayer 1340, e.g., an undoped amorphous silicon layer, is disposedbetween the first doped layer 1330 and an oppositely doped second dopedlayer 1350, e.g., a p-doped amorphous silicon layer. The first dopedlayer 1330, intrinsic layer 1340, and second doped layer 1350 form theactive region 1370 of the p-i-n diode 1300. A second electrode layer1360 is disposed over the second doped layer 1350.

The second electrode layer 1360 substantially transmits the stimuluslight that turns on the photodiode 1300. For example, the secondelectrode layer 1360 may have an optical transmittance greater than 50%at wavelengths of the stimulus light. Suitable materials for the secondelectrode layer 1360 include conductive oxides such as indium tin oxide(ITO), conductive polymers, metal grids, carbon nanotubes (CNT),graphene, wire meshes, thin metal films and/or other conductors thathave the requisite optical transmittance. The device 1300 may include anoptical filter that narrows the band of wavelengths of light that reachthe active region. For example, in some embodiments the second electrodelayer, e.g., ITO layer, having a suitable thickness provides an opticalfilter that substantially attenuates wavelengths of light that areoutside a wavelength band of the desired trigger stimulus andsubstantially passes wavelengths of light that are within the wavelengthband of the desired trigger stimulus.

The second electrode layer 1360, second doped layer 1350, and intrinsiclayer 1340 extend over the substrate 1310 and form a second lead 1334 ofthe photodiode 1300. In some embodiments, the first doped layer 1330 isan n-doped layer and comprises n-doped amorphous silicon (a-Si), thesecond doped layer 1350 is a p-doped layer and comprises p-doped a-Siand/or the intrinsic layer comprises intrinsic a-Si. The example ofFIGS. 13A and 13B illustrates a p-i-n diode, however, it will beappreciated that in some embodiments a photodiode may be formed by a pnjunction without the intrinsic layer.

In some embodiments the intrinsic layer 1340 of the p-i-n photodetectoris a 600 nm-thick intrinsic a-Si deposited by plasma-enhanced chemicalvapor deposition (PECVD). The n-layer 1330 is a 120 nm-thickphosphorous-doped a-Si deposited by PECVD, and the p-layer 1350 is a 20nm-thick boron-doped a-Si deposited by PECVD. This top-side p-layer 1350is designed to be very thin in order to minimize optical absorption ofthe light being detected. The n-electrode 1320 is a 200 nm-thick MoCralloy deposited by sputtering, and the p-electrode 1360 is a 55 nm-thickindium-tin-oxide (ITO) designed with an optical thickness optimal fortransmitting the wavelength of light being detected.

In some embodiments, the first 1333 and second 1334 leads electricallyconnect the active region 1370 of the photodiode 1300 to the switch,power supply and/or heater wherein both the sensor and the switch of thetrigger circuitry are disposed on the surface of the frangible substrate1310.

In some embodiments, the first 1333 and second 1334 leads electricallyconnect the active region of the photodiode 1300 to a periphery of thesubstrate 1310. For example, the leads 1333, 1334 may be configured tobe connected to external wires that communicate with one or moreexternally located electronic devices, e.g., the power source andswitch, which are not disposed on the substrate 1310. In someembodiments, the first electrode layer 1320 (first lead 1333) and theheater are made of the same materials.

An adhesion promoting surface 1315, such as a barrier layer, mayoptionally be disposed between the substrate 1310 and the firstelectrode layer 1320 and or intrinsic layer 1340 of the photodiode 1300and/or the heater. In one embodiment, the barrier layer comprises a 300nm-thick PECVD deposited SiO2 barrier layer that enhances film adhesionto the ion-rich surface of the stress-engineered substrate. In somescenarios, the intrinsic layer 1340 (intrinsic a-Si) shown in FIG. 13Amay not stick well to the frangible substrate 1310, and in thesescenarios the film stack would crack if the barrier layer 1315 is notdeposited on the frangible substrate 1310 before the intrinsic layer1340 is deposited. Without the barrier layer 1315, the frangiblesubstrate 1310 may cause bubbling at the interface between the substrate1310 and the photodetector layers 1320, 1340. Suitable materials for thebarrier layer 1315 include one or more of silicon dioxide (SiO2),silicon nitride (SiN), and silicon oxynitride (SiON). The barrier layer1315 may have a thickness greater than 300 nm, greater than 500 nm orbetween 200 and 700 nm, for example.

In some embodiments, the desired trigger stimulus is light from a lowpower conventional hand-held laser pointer typically used for makingpresentations. Typical wavelengths are either 532 nm (green) or 650 nm(red). The self-destruct sequence is activated by aiming the laserpointer on the photodetector 1300 from a distant location. Thephotodetector 1300 may be designed to have a large dynamic response, soit causes the electronic switch to trigger reliably when theself-destruct light trigger stimulus is detected, but not when exposedto normal ambient light. This performance feature is achieved bychoosing an appropriate combination of layer thicknesses and activeregion area.

The area of the active region has to be large enough so it can be easilyseen and targeted with a laser pointer from a distance of, for example,up to 15 feet. However, if the area is too big, the photocurrent causedby ambient light could be so large that it triggers the self-destructprocess. In some embodiments, the photodetector can have active areasize of 3 mm×3 mm in combination with the i and p a-Si layer thicknesschoices tabulated in Table 1 which provides an exemplary layer structureof an integrated thin film photodetectors sensor at the active regiondisposed on an ion exchanged glass frangible substrate.

TABLE 1 Thickness Layer Material/process  550 Å p electrode ITO tunedfor green light,/sputtered  200 Å p doped a-Si Boron doped/PECVD 6000 Åintrinsic a-Si /PECVD 1200 Å n doped a-Si Phosphorus doped/PECVD 2000 Ån electrode MoCr/sputtered 3000 Å barrier Oxide/PECVD Ion exchangedglass frangible substrate

FIG. 14 shows the photocurrent response when the 3 mm×3 mm photodetectoris in the dark, exposed to ambient light in a bright fluorescent-litroom, illuminated with a bright cell phone LED flashlight at closeproximity, and when illuminated with a typical 5 mW green laser pointer.The contrast in photocurrent response between ambient light and triggerlight exceeds 2 orders of magnitude, so the device architecturedisclosed herein allows a wide design margin for choosing a thresholdphotocurrent that determines when the self-destruct switch is triggered.For example, in some embodiments, the self-destruct switch can bedesigned to trigger to connect the power source to the heater when thephotocurrent is about twice the expected maximum photocurrent producedby the ambient environment of the sensor.

In some embodiments, the photodetector is fabricated so theelectrodes/leads are formed together with the active layers in aself-aligned fashion, allowing the complete device, including electricalrouting leads that connect the active region to the periphery of thesubstrate, to be made with not more than two masking layers. FIG. 15 isa flow diagram that illustrates a process of making the photodetector inaccordance with some embodiments. FIGS. 16A, 16B, and 13Bdiagrammatically depict top views that illustrate the process of makingthe photodetector.

The photodetector may be formed by first depositing an optional barrierlayer on a stress-engineered substrate. A first electrode layer is thendeposited 1510 on the barrier layer. In some embodiments, the firstelectrode layer comprises a MoCr alloy that is sputtered on the barrierlayer. A first doped semiconductor layer is deposited 1520 on the firstelectrode layer. The first doped layer may be an n-doped a-Si layerdeposited by PECVD, for example. The first doped semiconductor layer andthe underlying first electrode layer are then patterned 1530 to form thefirst electrode region, e.g., by photolithographic patterning of thefirst electrode layer/first doped layer stack through a first maskingstep followed by CF4 plasma etching of the first doped layer andchemical wet etching of the first electrode layer.

FIG. 16A shows a top view of the first electrode region 1601 comprisingthe first electrode/first doped semiconductor layer stack after thefirst patterning step. An intrinsic layer, e.g., intrinsic a-Si and asecond, oppositely doped layer, e.g., p-doped a-Si, are deposited 1540above the patterned first electrode region, e.g. by PECVD. The secondelectrode layer is deposited 1550 above the second doped layer. Forexample, the second electrode layer may comprise ITO deposited bysputtering. The second electrode layer is patterned 1560, e.g., byphotolithographic exposure through a second mask followed by chemicaletching with HCl acid according to the pattern 1602 in FIG. 16B. Theintrinsic and second doped layers are etched, e.g., with CF4 plasma,also using the second mask. This second patterning step not onlypatterns the second doped and intrinsic layers in the active region, butalso selectively removes the remaining portions of the first doped layerabove the first electrode layer in the first electrode region formed inthe previous patterning step. The end result is the device 1300 shown inFIGS. 13A and 13B, where the electrodes can be formed together with theactive region in a self-aligned manner in only two masking steps. Insome embodiments the first electrode layer and the heater can be formedsimultaneously from the same materials. Additional information relatedto the formation of sensor and heater structures for initiating fractureof a frangible substrate is discussed in U.S. patent application Ser.No. 15/220,221 filed on Jul. 26, 2016 which is incorporated herein byreference.

Embodiments discussed herein involve a frangible substrate, e.g., afrangible glass substrate, that is pre-weakened at select locations. Insome embodiments, the pre-weakening is accomplished by sending adamaging electrical pulse to a heater. For example, the electrical pulsemay be applied as part of the fabrication process. The pulse shape,duration, and/or amplitude are controlled so they produce a desiredamount of damage to the substrate but are insufficient to initiateself-destruction of the substrate. The amount of energy needed toinitiate fracture of a frangible substrate having a pre-weakened areacan be substantially reduced when compared to a substantially similarsubstrate that does not include a pre-weakened area.

EXAMPLES

Examples discussed below employ one or two pre-conditioning current topre-weaken the substrate. Other embodiments may employ different numberof electrical pulses. The number of pulses can be used as a way tocontrol the amount of pre-weakening desired, which could vary dependingon the application. Examples 1 and 2 discussed below involve squarepulses. However, other pulse shapes such as triangular, sawtooth, orsinusoidal shapes provide additional degrees of freedom for controllingthe pre-weakening process. The effect on the substrate of the electricalimpulse applied to the heater depends on the overall combination of thenumber of pulses, the pulse shape, duration, and/or amplitude of thepulses. Thus, one or more of these parameters can all be tunedseparately or together to attain the desired degree of damage. In someembodiments, the conditioning pulse applied to the heater can be avoltage pulse, instead of a current pulse. In some embodiments, asdiscussed above, the electrical pulse to the heater can be initiated bya wireless radio frequency, signal, a microwave signal, or other triggerstimulus. The pre-weakening can be applied at strategic locations otherthan or in addition to areas directly under the heater.

Example 1

In a first example, an integrated thin film resistive heater was used topre-weaken and to initiate the break-up of a frangible glass substrate.FIG. 17 shows the example device 1700 comprising a frangible substrate1710 and two integrated heaters 1721, 1722 disposed at opposite ends ofthe substrate 1710. In this example, the heaters are 3.6 μm-thick Mgthin films deposited by sputtering and patterned to form rectangularstrips with bow tie-shaped electrodes. When current is applied acrosselectrodes 1723, 1725 and electrodes 1724, 1726, intense heat isgenerated at the narrow stripe sections 1727, 1728 of the thin filmheaters 1721, 1722. The heat damages the underlying frangible glasssubstrate 1710 initiating a fracture point that causes the entirefrangible glass substrate 1710 to self-destruct along with heaters 1721,1722.

Pre-weakening the substrate can reduce the amount of electrical powerand energy needed to initiate self-destruction of the substrate 1710. Afrangible glass substrate with one or more pre-weakened areas cansubstantially reduce the energy required to initiate fracture whencompared to a similar substrate without one or more pre-weakened areas.In these examples, pre-weakening involves damaging an area with acontrolled electrical pulse to the resistive heater as part of thefabrication process. The pulse shape, amplitude, and duration are set sothe electrical impulse generates sufficient heat to damage and weakenthe target area but does not cause the heater to fuse (break) or causethe underlying frangible glass substrate to self-destruct. t

In Example 1, the controlled electrical pulse was set so the shape andamplitude match the parameters that the heater would experience inactual operation. The pulse was then cut short just before the expectedtime duration when the heater would normally fuse. FIG. 18 shows theelectrical trace signals of a pulse used to condition an exemplary 3mm×0.5 mm heater (corresponding to the heater 1722 in FIG. 17 ). In thisexample, the electrical pre-weakening reduced the amount of energyrequired to initiate fracture by about 23%, from 5.25 Joules to 4.05Joules. In this example, the conditioning pulse 1801 was single square 3amp current pulse lasting 0.9 sec. Curve 1802 in FIG. 18 represents themeasured voltage across the heater. The voltage increases with pulseduration because the resistance of the Mg film increases as thetemperature rises with time.

FIG. 19 shows the electrical characteristics of the pulse-conditionedheater when operated so the applied stimulus causes the heater to fuseand the substrate to fracture. Curve 1901 represents the measuredcurrent through the heater, and curve 1902 represents the measuredvoltage across the heater. Curve 1903 is a monitor signal used fordetecting when the substrate factures. The monitor signal is designed soits output voltage is initially 7V but transitions abruptly to 0V uponsubstrate disintegration. With 3 amps of trigger current, the heaterfuses in 0.78 sec and the glass fractures in 3.53 sec. The total triggerenergy consumed is 4.05 Joules. These values compare to a requiredenergy of 5.25 Joules, a heater fusing time of 0.98 sec, and a glassfracture time of 3 sec for an identical system not preconditioned withan electrical pulse.

Example 2

In this example, the device comprised 3 mm long×1 mm wide heaters. Suchlarger heaters can be used for fracturing thicker frangible glassbecause thicker glass requires the higher energies that only largerheaters can deliver. For this larger heater, a pre-conditioning pulsecurrent of 4.7 amps, applied twice for durations of 1 sec. per pulse.Once activated with the double pulse impulse, the energy needed tofracture the glass was 5.8 Joules. The corresponding time for the heaterto fuse was 0.59 sec, and the time for the glass to fracture was 1.41sec.

Without the pre-conditioning treatment, applying an identical electricalstimulus did not cause the heater to fuse or the glass to fracture evenwhen held for over 1 sec. The energy needed to initiate fracture wasover 9.8 Joules, so the pulse treatment reduced the required energy byover 40% in this example.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein. The use of numerical ranges by endpointsincludes all numbers within that range (e.g. 1 to 5 includes 1, 1.5, 2,2.75, 3, 3.80, 4, and 5) and any range within that range.

Various modifications and alterations of the embodiments discussed abovewill be apparent to those skilled in the art, and it should beunderstood that this disclosure is not limited to the illustrativeembodiments set forth herein. The reader should assume that features ofone disclosed embodiment can also be applied to all other disclosedembodiments unless otherwise indicated. It should also be understoodthat all U.S. patents, patent applications, patent applicationpublications, and other patent and non-patent documents referred toherein are incorporated by reference, to the extent they do notcontradict the foregoing disclosure.

The invention claimed is:
 1. A method, comprising: disposing a heater onor proximate to a frangible substrate such that the heater is thermallycoupled to the frangible substrate, the frangible substrate comprisingat least one pre-weakened area and a non-pre-weakened area; andpre-conditioning the frangible substrate at or proximate to a locationof the heater, wherein the pre-conditioning weakens the substrate at thepre-weakened area relative to the non-pre-weakened area without causingpropagating fractures in the frangible substrate and wherein applicationof a predetermined level of energy to the heater initiatesself-destruction of the frangible substrate by fractures propagatingfrom the pre-weakened area and causing the frangible substrate tofracture; wherein pre-conditioning the frangible substrate comprisesactivating the heater by an energy source at an energy lower than athreshold energy that initiates fractures in the pre-weakened area. 2.The method of claim 1, wherein pre-conditioning the frangible substratecomprises applying to the frangible substrate less than 60% and morethan 5% of the threshold energy that initiates fractures in thepre-weakened area.
 3. The method of claim 1, wherein pre-conditioningthe frangible substrate comprises one or more of thermally,electrically, optically, chemically, and mechanically pre-conditioningthe frangible substrate.
 4. The method of claim 1, whereinpre-conditioning the frangible substrate comprises forming one or moreof pits, holes, and patterns on the substrate by one or more of chemicaletching, plasma etching, ion milling, physical machining, and laserablating the frangible substrate.
 5. The method of claim 1, furthercomprising activating the heater to initiate propagation of fractures inthe pre-weakened area.
 6. The method of claim 5, wherein activating theheater comprises applying a predetermined amount of energy to theheater.
 7. The method of claim 6, wherein the predetermined amount ofenergy is less than 60% of a threshold energy that initiates fracturesin the pre-weakened area.
 8. The method of claim 6, wherein the heateris a resistive heater and applying the predetermined amount of energy tothe heater comprises applying current through the resistive heater. 9.The method of claim 1, wherein the heater comprises one of a resistiveconductive film, a microwave absorber, and an optical absorber.
 10. Themethod of claim 1, wherein one or more electronic circuits are disposedon the non-pre-weakened area of the frangible substrate such that thefractures in the frangible substrate also fracture the electroniccircuits.
 11. A method, comprising: generating heat by a heater disposedon or proximate to a frangible substrate such that the heat is thermallycoupled to the frangible substrate, the frangible substrate having atleast one pre-weakened area and a non-pre-weakened area;pre-conditioning the frangible substrate at or proximate to a locationof the heater to weaken the substrate at the pre-weakened area relativeto the non-pre-weakened area, wherein pre-conditioning the frangiblesubstrate comprises activating the heater by an energy source at anenergy lower than a threshold energy that initiates fractures in thepre-weakened area; and applying a predetermined level of energy to theheater sufficient to initiate self-destruction of the frangiblesubstrate by fractures propagating from the pre-weakened area andcausing the frangible substrate to fracture.
 12. The method of claim 11,wherein the fractures cause the frangible substrate to break intopieces.
 13. The method of claim 11, wherein applying the predeterminedlevel of energy to the heater results in applying less than 60% of athreshold energy to the frangible substrate that initiates fractures inthe pre-weakened area.
 14. The method of claim 11, wherein thepre-weakened area comprises at least one of a thermally, optically,electrically, chemically, or mechanically pre-conditioned area.
 15. Themethod of claim 11, wherein the pre-weakened area comprises one or moreof pits, holes, and patterns formed on the frangible substrate.
 16. Themethod of claim 11, wherein the frangible substrate comprises glass. 17.The method of claim 11, wherein the frangible substrate comprises atleast one tensile stress layer having a residual tensile stress and atleast one compressive stress layer having a residual compressive stressand being mechanically coupled to the at least one tensile stress layersuch that the at least one tensile stress layer and the at least onecompressive stress layer are self-equilibrating.
 18. The method of claim11, wherein the heater comprises one of a resistive conductive film, amicrowave absorber, and an optical absorber.
 19. The method of claim 11,wherein one or more electronic circuits are disposed on thenon-pre-weakened area of the frangible substrate such that the fracturesin the frangible substrate also fracture the electronic circuits.